Despite the many advances in dentifrice formulation in recent years, there is still a need for improved products. Since the development of anticaries agents, especially the fluorides, has led to a decline in the incidence of tooth caries, attention in the oral health care field has increasingly focused on the problems of gum disease, periodontitis. While antibacterial agents have been proposed for inclusion in products for use by consumers in the treatment of periodontitis, certain problems have been associated with their use. For example, use of chlorhexidine, which has been known as an antibacterial agent, has been associated with staining problems. It produces yellow to dark brown stains on teeth, tongue and oral mucosa. Furthermore, chlorhexidine has a very bitter taste. Cationic antibacterial agents other than chlorhexidine, such as hexetidine, alexidine, and other quaternary ammonium compounds, also cause staining.
There has been a need, therefore, for developing a dentifrice formulation including chlorhexidine or other antibacterial agents, which does not cause staining of the teeth and which has an improved taste. Moreover, dentifrices having improved anticavity effects are still desired.
Staining can be troublesome, whether or not chlorhexidine is the cause. The accumulation of stains on tooth surfaces poses an esthetic problem for many individuals. Staining is promoted by dietary substances such as coffee, tea and red wines, and by smoking.
Plaque is a common factor in caries, gum disease and staining and greatly contributes to their development. Proper oral hygiene as currently practiced requires that plaque be removed or prevented not only for cosmetic purposes but also to eliminate a source of potential injury to teeth and gums.
Plaque is initiated when cariogenic bacteria adhere to pellicle, a proteinaceous film on the surface of teeth. These adherent bacteria metabolize dietary constituents, reproduce and accumulate to form the tenacious deposit known as plaque. Plaque generally consists of bacteria, bacterial end products such as polysaccharides, inorganic salts and salivary proteins. Plaque bacteria ferment dietary carbohydrates to organic acids which demineralize enamel, resulting in tooth decay.
Plaque acts as a nucleus for the formation of calculus (tartar) which is essentially plaque that has been mineralized with calcium phosphate salts. As calculus matures and hardens, it tends to stain noticeably due to adsorption of dietary chromagens. In addition to their unattractive appearance, calculus deposits, at the gum line, are a contributing source of gingivitis and periodontal disease.
Silicones have previously been suggested for inclusion in dentifrice compositions in that it has been proposed that they would coat the teeth and thereby prevent cavities and staining. For example, British Patent Specification 689,679 discloses a mouthwash containing an organopolysiloxane for the purpose of preventing adhesion of, or for removal of, tars, stains, tartar and food particles from the teeth. However, polymers such as those disclosed in the '679 specification have not generally been successfully used for coating the teeth since it has been found that the polysiloxane does not adhere to the teeth for prolonged periods of time. Therefore, the need for dentifrice formulations including a hydrophobic substance which effectively coats the teeth has not been satisfied.
Yetter U.S. Pat. No. 3,624,120 discloses quaternary ammonium salts of cyclic siloxane polymers, which are said to be useful as cationic surfactants, as bactericides and as anticariogenic agents. Yetter indicates that it is believed that the siloxane polymer absorbs onto calcium phosphate to form a film which decreases the rate of acid solubilization. However, due to the solubility of the cyclic, low molecular weight, high N/Si ratio compounds of Yetter, it would not be expected that they could impart a strongly hydrophobic film to the surface of teeth. Moreover, there does not appear to be any disclosure in Yetter that its low molecular weight compounds would have any usefulness in preventing staining. Other problems with the Yetter compounds are their high cost due to the high N/Si ratio. Also, the freedom from toxicity of high N/Si ratio compounds may be questioned.
Viccaro, et al. copending application Ser. No. 07/276,704 filed simultaneous herewith and entitled "Dentifrice Containing Aminoalkyl Silicones" discloses dentifrice formulations including aminoalkylsilicones for coating the teeth and inhibiting stain and caries. The aminoalkylsilicones have been found to be more substantive than alkylsilicones, apparently due to the interaction of the positively charged nitrogen of the amine with the negative charges on the surfaces of the teeth. However, amine groups tend to react with certain chemical groups found in dentifrice components such as the aldehydes of flavoring ingredients. Consequently, aminoalkylsilicones bearing amine groups capable of being protonated over a broad pH yet of reduced reactivity are desirable.
Attempts have been made to modify the structure of aminosilicones to decrease the reactivity of the amino groups. In U.S. Pat. No. 4,507,455 aminosilicones are reacted with acetic anhydride to form amides. It is believed that this modification seriously limits the pH range over which the amines will be protonated, thereby detracting from the usefulness of the respective aminoalkylsilicones in applications, such as those mentioned above, wherein protonation of the amine is significant. Also, U.S. Pat. No. 4,472,566 discloses the reaction of aminosilicones with benzylchloride to yield secondary and tertiary amines.
Morehouse U.S. Pat. No. 3,032,577 discloses organosiloxanes which are said to be useful for a variety of applications in the synthetic polymer art, particularly as flocculating agents for aqueous dispersion of clay. The organosiloxanes of the Morehouse patent include units of the formula: ##STR1## wherein --OZ-- is the divalent group derived from a monoepoxide by opening of the oxirane ring, HO is interconnected to N through 2 carbon atoms, a is an integer from 0 to 1, n is an integer from 3 to 15, R may be hydrogen, monovalent hydrocarbon or ##STR2## Morehouse does not appear to indicate that his compounds would be useful in dentifrices and the like, nor does he seem to recognize the desirability of using compounds which can yield a higher positive charge density.